The dermatologist gave me a prescription for doxycycline and Differin beginning in late May and by July my face was free of acne (though it was still oily and filled with red marks, etc). During the fall, I took the antibiotic for about 10 days at a time only when my face appeared to be developing cysts. By January, I noticed that it had become a lot less effective. This summer I started taking Keflax which works well, but obviously it would be better if I didn't have to take oral medications. My face still breaks out all the time, but it's never been as bad as it was before I was prescribed the doxycyline and Differen.